Since its a sibling, and siblings tend to be in a person's close circle of people, informal speech is used.
Arrogant due to his fortune and growing up around similar characters. Snobbish due to mistreatment perhaps from a close friend in his childhood. And above all, honest, which may be a product of good upbringing and certainly insight on his true character.
If you are critical of someone or something, you show that you disapprove of them.
